Fluoride capture from wastewater

Abstract

One example provides a method of recovering fluoride from wastewater with a first, higher concentration of fluoride. The method comprises adding a metal cation to the wastewater that reacts with fluoride in the wastewater to form a precipitate comprising a fluoride compound that is less soluble in water than lithium fluoride to produce treated wastewater with a second, lower concentration of fluoride; and recovering the precipitate.

1 . A method of recovering fluoride from wastewater with a first, higher concentration of fluoride, the method comprising:
 adding a metal cation to the wastewater that reacts with fluoride in the wastewater to form a precipitate comprising a fluoride compound that is less soluble in water than lithium fluoride to produce treated wastewater with a second, lower concentration of fluoride; and   recovering the precipitate.   
     
     
         2 . The method of  claim 1 , wherein the metal cation is added as a salt or from a mineral source. 
     
     
         3 . The method of  claim 1 , wherein the metal cation comprises calcium, and the precipitate is calcium fluoride. 
     
     
         4 . The method of  claim 1 , wherein the metal cation comprises one or more of aluminum, magnesium, boron, or a transition metal. 
     
     
         5 . The method of  claim 1 , further comprising adding a base to the wastewater to adjust a pH of the wastewater. 
     
     
         6 . The method of  claim 5 , wherein the base comprises an organic base that can be decomposed using one or more of heat or oxygen. 
     
     
         7 . The method of  claim 5 , wherein the base is a Lewis base that can accept fluoride. 
     
     
         8 . The method of  claim 1 , further comprising adding an acid to the wastewater to adjust a pH of the wastewater. 
     
     
         9 . The method of  claim 8 , wherein the acid comprises an organic acid that can be decomposed using one or more of heat or oxygen. 
     
     
         10 . The method of  claim 1 , wherein the method is performed as a continuous flow process. 
     
     
         11 . The method of  claim 1 , wherein adding the metal cation to the wastewater comprises flowing the wastewater over a solid bed comprising an excess of the metal cation. 
     
     
         12 . The method of  claim 1 , wherein adding the metal cation to the wastewater comprises adding a solution containing the metal cation to the wastewater. 
     
     
         13 . The method of  claim 12 , wherein adding the solution containing the metal cation to the wastewater comprises titrating the wastewater with the solution containing the metal cation. 
     
     
         14 . The method of  claim 1 , further comprising recovering the wastewater with the second, lower concentration of fluoride, and using the wastewater with the second, lower concentration of fluoride in a battery recycling process. 
     
     
         15 . The method of  claim 14 , wherein the wastewater with the second, lower concentration of fluoride comprises lithium hydroxide. 
     
     
         16 . A system for recovering fluoride from wastewater with a first, higher concentration of fluoride, the system comprising:
 an inlet configured to admit the wastewater;   a reaction volume configured to receive the wastewater from the inlet and contain the wastewater as the wastewater is exposed to a salt, the salt comprising a metal cation that reacts with the fluoride in the wastewater to form a precipitate that is less soluble in water than lithium fluoride; and   an outlet configured to emit treated wastewater with a second, lesser concentration of fluoride.   
     
     
         17 . The system of  claim 16 , wherein the reaction volume is a continuous flow reactor. 
     
     
         18 . The system of  claim 16 , wherein the reaction volume comprises a solid bed containing an excess of the salt. 
     
     
         19 . The system of  claim 18 , wherein the salt comprises a calcium salt. 
     
     
         20 . The system of  claim 16 , further comprising an acid inlet operable to add an acid to the wastewater to adjust a pH of the wastewater. 
     
     
         21 . The system of  claim 16 , further comprising a base inlet operable to add a base to the wastewater to adjust a pH of the wastewater. 
     
     
         22 . The system of  claim 16 , wherein the outlet is connected to an inlet of a reactor used in a battery recycling system.